Anaerobically hardenable sealing compound composition

ABSTRACT

An anaerobic curable sealant composition is disclosed which is suitable as a fluid gasket for use in portions to be sealed in the field of automobile parts for example and which is superior in oil resistance and flexibility, the flexibility being retained even in a high-temperature atmosphere. 
     The composition is prepared by adding core-shell fine particles consisting of a core of a rubbery polymer and a shell of a glassy polymer to an anaerobic curable sealant comprising a urethane (meth)acrylate prepolymer, a radical-polymerizable monomer and an organic peroxide. It has a repulsive force high enough to retain flexibility and sealability capable of coping with vibrations and external stresses induced in a seal portion and is superior in oily surface adhesion.

FIELD OF THE INVENTION

The present invention relates to an anaerobic curable sealantcomposition and more particularly to an anaerobic curable sealantcomposition useful as a fluid gasket for forming a seal between twosurfaces of flanges which are large in the amount of displacement. Theanaerobic curable sealant composition of the present invention isemployable usefully especially as a fluid gasket for preventing theleakage of a lubricating oil in various industrial machines and devicessuch as internal combustion engines and drive units.

PRIOR ART

Heretofore, in the fields of automobile parts, electric parts andvarious mechanical parts, as a method for bonding and sealing componentsto be sealed on an assembly line there has been adopted a method whereinsealing surfaces are pressure-welded through a molded gasket or a methodwherein sealing surfaces are sealed through a fluid gasket.Particularly, as to the latter method using a fluid gasket, an FIPG(Formed In Place Gaskets) method, in which sealing surfaces are sealedunder automatic application of a liquid sealant using a robot or thelike on an assembly line, is most popular because of high productivity,low cost and highly reliable sealing performance. As an FIPG theremainly is used an anaerobic gasket containing as main components a roomtemperature curing type silicone material (silicone RTV) which reactswith moisture contained in the air and cures and a urethane(meth)acrylate which cures in a short time upon contact with metallicsurfaces after shutting out oxygen by sandwiching a sealant in betweenflange surfaces. Particularly, silicone RTV is presently in use mostwidely because of its high heat resistance and excellent workability andadaptability to coated flange surfaces.

In the FIPG using silicone RTV, however, with upgrading of various oils,including engine oil, the damage to silicone rubber caused by oils hasbeen becoming more and more serious and the attainment of a highresistance to oil is now a problem to be solved.

Particularly, as to oils used in automobiles or the like, an acrylicanaerobic curable sealant has come to be used. This sealant, because ofan acrylic type, involves the drawback that it is poor in flexibility ascompared with silicone compositions. The sealant is required to possessflexibility sufficient to cope with vibrations and stresses in a sealingportion including flanges or the like and also possess a repulsive forcesufficient to retain sealability. It is difficult to consider that theacrylic anaerobic curable sealant satisfies these characteristicsrequired. Thus, this sealant is unsatisfactory in actual use, and it isthe actual situation that silicone RTV is used in most applications.

The flange of an oil pan is in many cases formed by combining differentmaterials such as iron and aluminum. Therefore, a large lateraldisplacement is apt to occur at the flange surface due to a differencein thermal expansion coefficient between both materials which is causedby a change in temperature of the engine portion. The sealant layer isrequired to exhibit a high follow-up performance for coping with suchdisplacement. This problem is serious especially in large-sized engines.The lateral displacement of the flange surface can be diminished byincreasing the thickness of the gasket, but this attempt gives rise toan extremely serious drawback that an anaerobic curing does not takeplace.

In view of this point, methods have been proposed to impart flexibilityto an anaerobic curable polymeric composition as an acrylic composition,such as a method of imparting flexibility to the composition itself byusing an urethane acrylate as acryl material and a high molecularprepolymer prepared by polymerizing a monomer which is a soft segmentof, say, a polyether in the main chain, and a method of impartingflexibility to the entire composition by adding a plasticizer orsynthetic rubber particles such as acryl rubber or butyl rubberparticles to an acryl polymerizable compound.

However, in the case of using a soft segment-containing high-molecularprepolymer, the flexibility of the composition is deteriorated when thecomposition is used in an atmosphere held at 120° C. or so, that is,when subjected to heat history. At a portion which becomes high intemperature the flexibility of sealant is lost with the lapse of time.In the synthetic rubber particles-added type, although flexibility isretained, there occurs a marked deterioration of solubility duringproduction, thus requiring a long time in the manufacturing process.Moreover, if the sealant is stored in a liquid state, the rubberparticles may be precipitated or agglomerated and clogged in the nozzleof an applicator. The use of a plasticizer gives rise to the drawbackthat the plasticizer oozes out from the sealant after curing.

In the conventional anaerobic curable fluid gasket, if engine oil, autotransmission fluid, or gear oil, is adhered to sealant bonding surfaces,there occurs a marked deterioration of bonding force. Usually, a moldrelease agent or an abrasive oil is adhered to the bonding surfaces andtherefore it is necessary to perform degreasing and washing with use ofan organic solvent or a detergent.

An anaerobic curable sealant composition is applied in an appropriateamount to sealing surfaces of flanges or the like, and when the sealingsurfaces are clamped, an oxygen-shut out portion polymerizes and curesto form a seal layer. However, when the amount of the composition to beapplied cannot be controlled precisely or when it is used in an excessamount for attaining a reliable sealing performance, the composition maybe forced out from the flange surfaces. The thus-exposed portion of theanaerobic curable sealant composition, which portion is in contact withair, does not cure. Therefore, it is necessary that the compositionshould possess a property not exerting a bad influence on thesurrounding materials.

Particularly when the anaerobic sealant composition is used in theengine and transmission of an automobile or the like, it is required inpractical use that the composition exposed from the flange bondingsurfaces and before curing should have a property of being disperseduniformly in the oils used. The anaerobic curable composition containingsynthetic rubber particles as a flexibility imparting agent is deficientin such dispersibility.

OBJECTS OF THE INVENTION

It is an object of the present invention to solve the above-mentionedproblems of the prior art and provide an anaerobic curable sealantcomposition superior in all of oil resistance, flexibility andsealability and capable of retaining excellent felxibility even aftersubjected to heat history.

SUMMARY OF THE INVENTION

The present invention resides in an anaerobic curable sealantcomposition comprising an urethane (meth)acrylate prepolymer, a radicalpolymerizable monomer, an organic peroxide, and core-shell fineparticles comprising a core of a rubbery polymer and a shell of a glassypolymer.

DETAILED DESCRIPTION OF THE INVENTION

An anaerobic curable sealant composition comprising an urethane(meth)acrylate prepolymer, a radical-polymerizable monomer and anorganic peroxide is already publicly known. The present invention ischaracterized by adding specific fine particles to the said compositionto improve the performance of the composition.

The urethane (meth)acrylate used in the present invention is aprepolymer having a urethane structure in its main chain and having(meth)acryloyloxy groups at its ends. This prepolymer is prepared byreacting a compound having two or more hydroxyl groups as functionalgroups with an organic compound having two or more isocyanate groups asfunctional groups to prepare a polyurethane prepolymer and introducing(meth)acryloyloxy groups into its molecular ends.

For example, the prepolymer in question is obtained by reacting aurethane prepolymer, which results from mixing and reacting a polyetherpolyol and an organic diisocyanate at a molar ratio in the range from1:1 to 1:2 in a diluting solvent, with a (meth)acryl monomer havingactive hydrogen in an amount sufficient to react with all of theremaining isocyanate groups in the said urethane prepolymer. Theurethane (meth)acrylate prepolymer may be used alone, or two or moresuch prepolymers may be mixed together and used. By the term“(meth)acrylate” is meant acrylate or methacrylate, and by the term“(meth)acryloyloxy group” is meant acryloyloxy group or methacryloyloxygroup. The term “oligomer” represents a dimer or a multimer having twoor more urethane bonds, including a polymer.

As to the molecular weight of the urethane (meth)acrylate prepolymer,the molecular weight of the resulting prepolymer can be selected freely,for example, by adjusting the molecular weight of a compound having twoor more hydroxyl groups as functional groups such as a polyether polyolor by adjusting the degree of reaction between a compound having two ormore hydroxyl groups as functional groups and a compound having two ormore isocyanate groups as functional groups. Usually prepared is aprepolymer of dimer to hectomer in terms of the degree ofpolymerization.

As the urethane (meth)acrylate prepolymer there may be used a publiclyknown one, as noted previously.

As the organic compound having two or more hydroxyl groups as functionalgroups for used in preparing the urethane prepolymer there may be usedany of various aliphatic polyols and aromatic polyols. Examples areethylene glycol, 1,2-propylene glycol, 1,3-butanediol, 1,4-butanediol,diethylene glycol, triethylene glycol, 1,6-hexanediol, neopentyl glycol,trimethylolpropane, glycerin, pentaerythritol, 1,2,6-hexanetriol,hydroxylated biphenol A, polyether polyol, and polyester polyol, with α,ω-diols being particularly preferred.

As the compound having two or more isocyanate groups as functionalgroups, which is the other component for use in preparing the urethaneprepolymer, there may be used any of various aliphatic polyisocyanatesand aromatic polyisocyanates. Examples are diphenylmethane diisocyanate,tolylene diisocyanate, naphthalene diisocyanate, xylene diisocyanate,and hexamethylene diisocyanate. Diisocyanates are particularlypreferred.

In the reaction of the compound having two or more hydroxyl groups asfunctional groups with the compund having two or more isocyanate groupsas functional groups, both compounds are used in such a manner that theisocyanate groups of the latter compound are in a proportion ofequimolar amount or more, i.e., NCO/OH≧1, preferably 1˜2, morepreferably 1.1˜1.7, relative to the hydroxyl groups of the formercompound. It is particularly preferred that isocyanate groups be presentat both ends of the urethane prepolymer.

Also as to the (meth)acryl monomer having active hydrogen for use in thereaction with the thus-prepared urethane prepolymer having isocyanategroups at both ends thereof, there may be used a known one. As examplesof active hydrogen sources are mentioned hydroxyl group, amino group,carboxyl group, and mercapto group. More concrete examples includehydroxyl-containing (meth)acrylates such as hydroxyalkyl(meth)acrylate,mercapto-containing (meth)acryaltes such as mercaptoalkyl(meth)acrylate,and (meth)acrylic acid. As alkyl groups are preferred those having 1 to6 carbon atoms. The thus-exemplified (meth)acryl monomer having activehydrogen is used in an amount sufficient to react stoichiometricallywith the isocyanate groups in the urethane polymer molecules.

The radical polymerizable monomer used in the present invention may alsobe a known one. Usually employed is a radical-polymerizable monomerhaving one polymerizable unsaturated bond. Particularly preferred is asubstituted or unsubstituted alkyl (meth)acrylate such as, for example,a (substituted) alkyl (meth)acrylate wherein the alkyl moiety has 1 to18 carbon atoms. Exampes are ethyl (meth)acrylate, n-propyl(meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate,t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate,isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl(meth)acrylate, n-lauryl (meth)acrylate, 2-methoxyethyl (meth)acrylate,2-ethoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, stearyl(meth)acrylate, tridecyl (meth)acrylate, 3-methoxypropyl (meth)acrylate,3,3-methoxymethylpropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,and hydroxypropyl (meth) acrylate. These radical-polymerizable monomersmay be used each alone or as a mixture of two or more.

The radical-polymerizable monomer is used in an amount of usually 1 to50 parts by weight, preferably 5 to 30 parts by weight, based on 100parts by weight of the urethane (meth)acrylate prepolymer.

The core-shell fine particles used in the present invention arecharacterized in that the core portion is constituted by a rubberypolymer and the shell portion by a glassy polymer. The particles have“elasticity” in the core portion and “hardness” in the shell portion anddo not dissolve in a liquid resin. The polymer which constitutes the“core” substantially has a glass transision temperature below theambient temperature, while the polymer which constitutes the “shell”substantially has a glass transition temperature above the ambienttemperature. The range of the ambient temperature is established as atemperature range in which the sealant is used.

According to a preferred method for producing the fine particles used inthe present invention, first the core portion is produced bypolymerizing a polymerizable monomer. As the polymerizable monomer theremay be used a known monomer insofar as the monomer affords a rubberypolymer. Examples are (meth)acrylate monomers such as n-propyl(meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth) acrylate,and n-decyl (meth)acrylate, aromatic vinyl compounds such as styrene,vinyltoluene, and α-methylstyrene, vinyl cyanide compounds such asacrylonitrile and methacrylonitrile, as well as monomers having onepolymerizable unsaturated bond such as vinylidene cyanide,2-hydroxyethyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate,2-hydroxyethyl fumarate, hydroxybutyl vinyl ether, monobutyl maleate,and butoxyethyl methacrylate. As further examples are mentioned ethyleneglycol di(meth)acrylate, butylene glycol di(meth)acrylate,trimethylolpropane di(meth)acrylate, trimethylolpropanetri(meth)acrylate, hexanediol di(meth)acrylate, hexanedioltri(meth)acrylate, oligoethylene di(meth)acrylate, oligoethylenetri(meth)acrylate, aromatic divinyl monomers such as divinylbenzene, andcrosslinkable monomers having two or more polymerizable unsaturatedgroups such as triallyl trimellitate and triallyl isocyanate. Thesepolymerizable monomers may be used each alone or as a mixture of two ormore insofar as they afford rubbery polymers. But the lattercrosslinkable monomers are usually employed in combination with theformer compounds.

Rubber properties vary depending on the molecular weight, molecularshape and crosslink density of the polymer prepared by polymerizing anyof the polymerizable monomers exemplified above. In the presentinvention it is required that the core portion be constituted by apolymer which is rubbery at room temperature. It is more preferable thatthe resulting polymer has a glass transition point of below −10° C.

Next, in the presence of the thus-prepared polymer particles as a core,there is performed a second polymerization involving polymerizing apolymerizable monomer to form a shell of a polymer which possessesglassy properties at room temperature. This polymerizable monomer may beselected from those exemplified previously as core forming monomers,provided it is required in the present invention that the polymer whichconstitutes the shell portion be glassy at room temperature. Preferably,the resulting polymer has a glass transition point of above 70° C. Thiscan be determined taking into account the molecular weight, molecularshape and crosslink density of the polymer obtained by polymerizing theselected polymerizable monomer. If the polymer which constitutes theshell portion is not glassy at room temperature, then when the polymerparticles are mixed into the radical-polymerizable liquid resin toprepare a sealant composition, the particles will be swollen by theradical polymerizable monomer, and with the lapse of time duringstorage, its viscosity will increase to form gels. That is, the storagestability will become low.

As preferred examples of the polymerizable monomer for forming the shellportion there are mentioned alkyl (meth)acrylates wherein the alkylmoiety has 1 to 4 carbon atoms, such as ethyl (meth)acrylate, n-butylacrylate, methyl methacrylate, and butyl methacrylate. These(meth)acrylates may be used each alone or in combination of two or more.Among them, methyl methacrylate is particularly preferred.

The amount of the core-shell fine particles is 0.1 to 80 parts byweight, preferably 5 to 65 parts by weight, based on the total amount of100 parts by weight of the urethane (meth)acrylate oligomer and theradical-polymerizable monomer. If the amount thereof is smaller than 0.1part by weight, it will be difficult to let the sealant compositionexhibit excellent flexibility when cured, and an amount thereofexceeding 80 parts by weight will lead to an extreme increase ofviscosity and deterioration of the storage stability. Particularlypreferred is an amount in the range of 10 to 40 parts by weight.

By the term “anaerobic” is meant a property which dislikes air, moreparticularly, a property such that stability and liquid state areretained in the presence of air or oxygen, but in the absence of air oroxygen there starts polymerization immediately. Anaerobic sealants haveheretofore been used for bonding and sealing metallic part and forpreventing looseness and fixing portions which are fitted together, andare thus publicly known. It is also publicly known that an anaerobiccurable composition comprises a radical-polymerizable monomer such as a(meth)acrylate, a prepolymer thereof, a polymerization initiator such asan organic peroxide, a curing accelerator, and a polymerizationinhibitor. Suitable such known components, including an organicperoxide, may be used in the present invention.

As examples of organic peroxides are mentioned such hydroperoxides ascumene hydroperoxide, t-butyl hydroperoxide, and diisopropylbenzenehydroperoxide, as well as diacyl peroxides, dialkyl peroxides, ketoneperoxides, and peroxy esters, with cumene hydroperoxide beingparticularly preferred in point of stability and curing speed.

The amount of the organic peroxide to be used cannot be limited becauseit depends on the balance among the kind of the peroxide used, curingtime and storage period, but is usually in the range of 0.01 to 10 partsby weight, preferably 0.1 to 5 parts by weight, based on the totalamount of 100 parts by weight of the urethane (meth)acrylate and theradical-polymerizable monomer.

In order for anaerobic curing to take place effectively, it is desirableto add a curing accelerator in addition to the organic peroxide.Examples of curing accelerators include organic sulfone imides, amines,and organometallic salts. As organic sulfone imides, o-benzoicsulfimides are preferred. As amines, diethylamine, triethylamine,N,N-dimethylparatoluidine, and 1,2,3,4-tetrahydroquinone are preferred.As examples of organometallic salts are mentioned copper chloride andcopper octylate. Where required, there may be added accelerators such assecondary and tertiary amines, stabilizers such as benzoquinone,hydroquinone, and hydroquinone monomethyl ether, polymerizationinhibitors such as phenols, and chelate compounds such asethylenediaminetetraactic acid (EDTA), sodium salts thereof, oxalicacid, acetylacetone, and o-aminophenols.

In the case where the flange material is an inert material such as aplastic material or where oxygen is present due to a large clearance,making anarobic curing difficult, it is recommended to apply a curingaccelerating primer beforehand to the flange surfaces to be bonded, thecuring accelerating primer containing a reducing agent for acceleratingthe decomposition of the organic peroxide to form radicals, wherebycuring can be allowed to take place in a short time.

As the curing accelerating primer which contains a reducing agent foraccelerating the decomposition of the organic peroxide to form radicals,it is desirable to use a primer which contains a condensate of analdehyde compound and a primary or secondary amine and/or an oxidizabletransition metal-containing compound. As examples of such condensate arementioned butylaldehyde-butylamine condensate, butylaldehyde-anilinecondensate, and acrolein-aniline condensate.

As examples of the oxidizable transition metal-containing compound arementioned organic compounds containing a transition metal selected fromthe group consisting of iron, cobalt, nickel and manganese, with metalchelates and complex salts being particularly useful. More concreteexamples are pentadione iron, pentadione cobalt, pentadione copper,propylenediamine copper, ethylenediamine copper, iron naphthenate,nickel naphthenate, cobalt naphthenate, copper naphthenate, copperoctenoate, iron hexoate, iron propionate, and acetylacetone vanadium.Substituted thioureas such as ethylenethiourea and benzothiazole arealso employable. For preparing the primer, it is preferable that theabove reducing compounds be dissolved in a proportion of 0.05 to 10 wt %in such organic solvents as toluene, acetone, methyl ethyl ketone, andalcohols.

Into the sealant composition of the present invention there may beadded, if necessary, various fillers such as fumed silica for theadjustment of viscosity, plasticizers, adhesion imparting agents such assilane compounds and phosphoric esters, and various known (meth)acrylicester monomers for the adjustment of rubber strength, including hardnessand elongation, such as isoborny (meth)acrylate, 2-hydroxyethyl(meth)acrylate, and 2-hydroxypropyl (meth)acrylate.

In the anaerobic curable composition of the present invention, sincefine core-shell particles are added as a functional filler to thecombination of the urethane (meth)acrylate prepolymer and theradical-polymerizable monomer, the flexibility of the composition doesnot deteriorate so markedly even under heat history, and the core-shellfine particles can be dispersed easily in the composition. Since thecore-shell fine particles have an oil absorbing property, the bondingforce of the composition is not deteriorated even on a surface with oilor the like adhered thereto. The anaerobic curable composition beforecuring, which contains the core-shell fine particles, is dispersedeasily in oil.

EXAMPLES

For easier understanding of the present invention, the invention will bedescribed in detail hereinunder by way of Examples thereof, which,however, do not restrict the scope of claim.

Preparing Sealant Compositions 1˜6

An urethane (meth)acrylate prepolymer UN-1101T (a product of NegamiKogyo Co.) having a polyether in the main chain thereof, an urethane(meth)acrylate prepolymer UN-2500 (a product of Negami Kogyo Co.) havinga polyester in the main chain thereof, and an epoxy acrylate SP-1507 (aproduct of Showa Kobunshi Co.), as urethane (meth)acrylate prepolymers,phenoxyethyl acrylate as a radical-polymerizable monomer, cumenehydroperoxide as an organic peroxide, ethylenediaminetetraacetic acid(EDTA) and butylhydroxytoluene (BHT) as stabilizers, saccharin,benzothiazole, n-dodecylmercaptan, and DAROCUR 1173 (a product of CibaGeigy Co.), as accelerators, silica as a filler, and F-351 (a product ofNippon Zeon Co.) and STAPHYLOID IM-101 (a product of Takeda ChemicalIndustries, Ltd.) as core-shell fine particles comprising a core of arubbery polymer and a shell of a glassy polymer, were used at suchweight ratios as shown in Table 1 to prepare compositions 1 to 6.

Preparing Sealant Compositions 7˜12 for comparison

Compositions 7 to 12 were prepared at such weight ratios as shown inTable 2, using the compounds used in the above preparation ofcompositions 1 to 6, provided some of them did not use the core-shellfine particles used in the above preparation of compositions 1 to 6, butinstead used ethylene-acryl rubber fine particles, liquidbutadiene-acrylonitrile, and bis-2-ethylhexyl phthalate (DOP) andethylene glycol as plasticizers.

Examples 1˜6 & Comparative Examples 1˜6:

Heat Deterioration Test

DAROCUR 1173 as an ultraviolet curing catalyst was added to thecompositions 1˜12, followed by radiation of ultraviolet light, toprepare about 2 mm thick sheets, from which were fabricated No. 2dumbbell specimens. The specimens thus fabricated were then subjected tocuring in a circulating hot air dryer at 120° C. and 150° C. for 240hours. Thereafter, the specimens were measured for percent elongation,the results of which are set out in Table 3.

Examples 7˜12 & Comparative Examples 7˜12:

Oily Surface Adhesion Test

The compositions 1 to 12 were measured for oily surface bonding forceunder shear. Specimens were prepared in the following manner. Bondingsurfaces of aluminum plates (A2024P)(size: 1.6×25×10 mm) defined by JISH4000 were polished with sand paper #240 and then washed with toluene.Auto transmission fluid was applied about 0.5 mg/cm² to one specimen.Then, each of the anaerobic curable compositions 1 to 12 was appliedonto the one specimen so as to protrude upon superposition of the otherspecimen thereon, and the specimens were superposed together 10 mm.Using two clothespins, the superposed surfaces were pinched form bothsides. The rate of pulling in the shear bonding force measurement wasset at 10 mm/min and the curing time was set at 72 hours. The resultsobtained are shown in Table 4.

Examples 13˜18 & Comparative Examples 13˜18:

Oil Dispersibility Test

200 ml of auto transmission fluid was put into a 500 ml glass beaker,into which was then added 0.2 g of each of the compositions 1 to 12,followed by agitation for 3 hours using a handy type agitator(revolutions: 500 rpm, agitating blades: propeller type, diameter: 50mm). After subsequent filtration using filter paper (500 mesh), a checkwas made visually to see if there was any residue. The results obtainedare shown in Table 5, in which the “◯” mark stands for the absence ofresidue, while the mark “X” stands for the presence of residue.

EFFECT OF THE INVENTION

The anaerobic curable composition of the present invention hasflexibility comparable to that of a silicone composition and has arepulsive force high enough to retain flexibility and sealabilitycapable of coping with vibrations and stresses induced in the sealportion between flanges for example. Thus, the follow-up performance ofthe sealant layer is high. Moreover, even when the composition is usedin a high-temperature atmosphere, it is possible to retain an excellentsealability without deterioration of flexibility.

The core-shell fine particles used in the present invention can beeasily dispersed as a functional filler in the composition, thus makingit possible to simplify the manufacturing process and reducing themanufacturing cost.

Further, since the anaerobic curable sealant composition of the presentinvention exhibits an oil absorbing action, its oily surface bondingforce is superior to that of the conventional flexibility-impartedanaerobic curable composition. More particularly, even if a lubricatingoil such as engine oil or auto transmission fluid, or a mold releaseagent used in molding, or a polishing oil or the like, is adhered to thesurface to be sealed such as a flange surface, it is not necessary toperform degreasing and washing with use of a solvent or a detergent.Thus, the manufacturing process can be so much simplified.

Additionally, the anaerobic curable composition before curing accordingto the present invention, which contains acryl type core-shell fineparticles, is dispersed in oil without agglomeration. Therefore, whenthe composition is used for sealing flange surfaces in an automobileengine or transmission, there is no fear that the portion of thecomposition protruded to the exterior from the flange surfaces may exerta bad influence on various oils. But the protruded portion will bedispersed uniformly in the oils.

TABLE 1 Composition Components 1 2 3 4 5 6 polyether-based urethane200.0 200.0 200.0 acrylate prepolymer polyester-based urethane 200.0200.0 200.0 acrylate prepolymer phenoxyethyl acrylate 50.0 50.0 50.050.0 50.0 50.0 EDTA stabilizer 0.4 0.4 0.4 0.4 0.4 0.4 BHT 0.5 0.5 0.50.5 0.5 0.5 Saccharin 2.5 2.5 2.5 2.5 2.5 2.5 benzothiazole 1.2 1.2 1.21.2 1.2 1.2 n-dodecylmercaptan 1.0 1.0 1.0 1.0 1.0 1.0 cumenehydroperoxide 5.0 5.0 5.0 5.0 5.0 5.0 silica 8.0 8.0 8.0 8.0 8.0 8.0core-shell rubber (1) 20.0 5.0 30.0 65.0 core-shell rubber (2) 30.0core-shell rubber (3) 30.0

TABLE 2 Composition Components 7 8 9 10 11 12 polyether-based urethane200.0 200.0 200.0 200.0 200.0 acrylate prepolymer epoxy acrylate 200.0phenoxyethyl acrylate 50.0 50.0 50.0 50.0 50.0 50.0 EDTA stabilizer 0.40.4 0.4 0.4 0.4 0.4 BHT 0.5 0.5 0.5 0.5 0.5 0.5 saccharin 2.5 2.5 2.52.5 2.5 2.5 benzothiazole 1.2 1.2 1.2 1.2 1.2 1.2 n-dodecylmercaptan 1.01.0 1.0 1.0 1.0 1.0 cumen hydroperoxide 5.0 5.0 5.0 5.0 5.0 5.0 silica8.0 8.0 8.0 8.0 8.0 8.0 core-shell rubber (1) 30.0 ethylene-acryl rubber20.0 20.0 liquid butadiene- 20.0 acrylonitrile DOP 10.0 ethylene glycol30.0

TABLE 3 Example/ Percent elongation Comparative Composition after 120°C. after 150° C. Example used Initially heat history heat history Ex. 1composition 1 138 127 110 Ex. 2 composition 2 135 119 95 Ex. 3composition 3 141 126 114 Ex. 4 composition 4 185 180 165 Ex. 5composition 5 170 160 128 Ex. 6 composition 6 153 127 110 Com.Ex. 1composition 7 120 100 75 Com.Ex. 2 composition 8 150 142 118 Com.Ex. 3composition 9 156 149 121 Com.Ex. 4 composition 10 145 120 93 Com.Ex. 5composition 11 50 15 9 Com.Ex. 6 composition 12 190 180 161

TABLE 4 Oily Surface Adhesion Test Example/ Shear Bonding ForceComparative oily degreased Example Composition used surface surface Ex.7 Composition 1 2.2 4.5 Ex. 8 Composition 2 2.6 5.1 Ex. 9 Composition 32.5 4.8 Ex. 10 Composition 4 3.2 4.0 Ex. 11 Composition 5 1.7 3.2 Ex. 12Composition 6 1.8 3.4 Com.Ex. 7 Composition 7 0.9 6.0 Com.Ex. 8Composition 8 0.8 3.2 Com.Ex. 9 Composition 9 0.6 3.4 Com.Ex. 10Composition 10 0.5 4.3 Com.Ex. 11 Composition 11 1.8 7.6 Com.Ex. 12Composition 12 0.5 2.2

TABLE 5 Oil Dispersibility Test Example/ Comparative Example Compositionused Evaluation Ex. 13 Composition 1 ∘ Ex. 14 Composition 2 ∘ Ex. 15Composition 3 ∘ Ex. 16 Composition 4 ∘ Ex. 17 Composition 5 ∘ Ex. 18Composition 6 ∘ Com.Ex. 13 Composition 7 ∘ Com.Ex. 14 Composition 8 XCom.Ex. 15 Composition 9 X Com.Ex. 16  Composition 10 ∘ Com.Ex. 17 Composition 11 ∘ Com.Ex. 18  Composition 12 X Note) “∘” stands for theabsence of residue. “X” stands for the presence of residue.

What is claimed is:
 1. An anaerobic curable sealant compositioncomprising a urethane (meth)acrylate prepolymer, a radical-polymerizablemonomer, an organic peroxide, and core-shell fine particles having acore of a rubbery polymer and a shell of a glassy polymer.
 2. Ananaerobic curable sealant composition as set forth in claim 1, whereinsaid urthane (meth)acrylate prepolymer is prepared by reacting anisocyanate group-containing urethane prepolymer with an activehydrogen-containing (meth)acryl monomer, said isocyanategroup-containing urethane prepolymer being prepared by reacting a polyolcompound with a polyisocynate compound at an excess molar ratio ofisocyanate groups relative to hydroxyl groups.
 3. An anaerobic sealantcomposition as set forth in claim 1, wherein said radical-polymerizablemonomer is a substituted or unsubstituted alkyl (meth)acrylate.
 4. Ananaerobic curable sealant composition as set forth in claim 1, whereinsaid rubbery polymer which constitutes the core of said core-shell fineparticles has a glass transition point of below −10° C., and said glassypolymer which constitutes the shell of the core-shell fine particles hasa glass transition point of above 70° C.
 5. An anaerobic curable sealantcomposition as set forth in claim 4, wherein said rubbery polymer whichconstitutes said core and said glassy polymer which constitutes saidshell each contain a (meth)acrylate monomer as an essential constituentmonomer.
 6. An anaerobic curable sealant composition as set forth inclaim 1, wherein said core-shell fine particles are present in an amountof 0.1 to 80 parts by weight based on the total amount of 100 parts byweight of both said urethane (meth)acrylate prepolymer and saidradical-polymerizable monomer.